Technical Field
The invention relates to a refractory product comprising chromium oxide, used in particular as internal lining of a gasifying reactor or “gasifier”.
State of the Art
A gasifier used for gasifying coal is known in particular. The process for the gasification of coal, which has been known for approximately fifty years, is currently undergoing strong growth. This is because it makes it possible, starting from very diverse hydrocarbon materials, for example coal, petroleum coke, biomass, wood, wood charcoal, indeed even heavy oils to be recycled, to produce synthesis gases which are used, on the one hand, as clean energy source and, on the other hand, as base compounds for the chemical industry. In addition, this process makes it possible to remove undesirable components, for example NOx, sulfur or mercury, before any discharge to the atmosphere.
The principle of gasification consists of a controlled partial combustion, under pressure and in the presence of steam or of oxygen, at a temperature of between 1000 and 1600° C. approximately.
Various types of gasifiers exist: fixed bed gasifiers, fluidized bed gasifiers or entrained bed gasifiers. These gasifiers differ in the method of introduction of reactants, the way in which the oxidant/fuel mixture is produced, the temperature and pressure conditions and the process for discharging the ash or liquid waste slag resulting from the reaction.
The article entitled “Refractories for Gasification” which appeared in the review “Refractories Applications and News”, Volume 8, Number 4, July-August 2003, written by Wade Taber of the Energy Systems Department of the Saint-Gobain Industrial Ceramics Division, describes the structure of an internal refractory lining of a gasifier. This gasifier is lined with different layers of refractory products capable of withstanding the conditions of temperature, pressure and chemical environment to which they are subjected during gasification. The layers of refractory products thus protect the internal metal wall of the gasifier from heat and from corrosion by the gases and slags.
The slags in gasifiers are typically composed of SiO2, FeO or Fe2O3, CaO and Al2O3. They may also comprise other oxides resulting from the materials which feed the gasifier. The basicity index B=(CaO+MgO+Fe2O3)/(Al2O3+SiO2) is typically approximately 0.6 and the ratio C/S=CaO/SiO2 is typically 0.4, the contents being as percentages by weight.
In order to increase the lifetime of the refractory linings, subjected to corrosion by slags and to thermal cycling, researchers have attempted to increase their thickness. However, this solution exhibits the disadvantage of reducing the working volume of the gasifier and thus its output.
James P. Bennett, in the article “Refractory liner used in slagging gasifiers” which appeared in the review “Refractories Applications and News”, Volume 9, Number 5, September/October 2004, pages 20-25, explains that the lifetime of the current refractory linings of gasifiers, in particular of the air-cooled systems, is very limited despite their high content of chromium oxide. He mentions in particular the report by S. J. Clayton, G. J. Stiegel and J. G. Wimer “Gasification Technologies, Gasification Markets and Technologies—Present and Future, an Industry Perspective”, US DOE, DOE/FE report 0447, July 2002.
FR 2 883 282 describes an internal refractory lining of a gasifier exhibiting at least one region made of a sintered material comprising, as percentages by weight, at least 40% of chromium oxide (Cr2O3) and at least 1% of zirconium oxide (ZrO2), at least 20% by weight of said zirconium oxide (ZrO2) being stabilized in the cubic and/or tetragonal form, the zirconium oxide being in particular stabilized with calcium oxide. This lining thus exhibits a better corrosion resistance.
WO 2008/109222 provides a treatment for the protection of the refractory products making up the refractory lining of gasifiers.
There exists an ongoing need for a refractory product exhibiting an even better resistance to corrosion by slags while satisfactorily withstanding the thermal shocks encountered inside gasifiers.
The aim of the invention is to meet this need.